Dim cn As New SqlConnection("Data Source=TANSENGCOSQLEXPRESS;Initial Catalog=MonitoringSystem;Integrated Security=True")
Dim cmd As New SqlCommand
Dim rd As SqlDataReader
Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
    cmd.Connection = cn
    cn.Open()
    cmd.CommandText = "SELECT username, password FROM tblUsers WHERE username = '" & txtUsername.Text & "' and password = '" & txtPassword.Text & "'"
    rd = cmd.ExecuteReader
    If rd.HasRows Then
        Me.Hide()
        frmMainMenu.Show()
    Else
        MsgBox("Invalid Credentials", MsgBoxStyle.Exclamation, "Invalid LogIn")
    End If
    cn.Close()
End Sub